SIMULATIONS OF NATURAL CONVECTION/RADIATION HEAT TRANSFER FOR HORIZONTAL AND VERTICAL ARRAYS OF HEATED RODS INSIDE A UNIFORM TEMPERATURE ENCLOSURE

In the current work, numerical simulations and experiments of an 8×8 square array of heater rods within an aluminum enclosure have been performed. This geometry represents the region inside the channel of a boiling water reactor (BWR) fuel assembly between two consecutive spacer plates. The simulation model and the experimental apparatus can be oriented horizontally or vertically, to represent transport or storage configurations. The interior void is filled with air at ambient pressure conditions. All rods dissipate at the same heating rate. In the experiment, this is controlled using a variable power supply. The temperatures are measured in the experiment by thermocouples that are placed within the enclosure walls, on the endplates, and in 31 of the 64 heater rods at their axial mid-planes. The three-dimensional computational fluid dynamics (CFD) model is based on the dimensions of experimental apparatus. Natural convection/radiation simulations are performed using the Fluent package at the same average wall temperatures and rates of heat generation measured from the experiment. Simulation results of rod temperatures are compared to experimental results to assess the accuracy of the threedimensional computational fluid dynamics (CFD) simulations. Simulation results show good agreement with measured temperatures. Average simulated rod temperatures are lower than measured data by up to 1.2% in horizontal orientation and higher than measured by up to 1.3% in vertical orientation.